Regular analysis of the primary coolant of a pressured water nuclear reactor is necessary to determine and measure the presence of a number of components, such as dissolved hydrogen and oxygen, chloride, total activity and boron. The primary cause of corrosion is, of course, the presence of oxygen dissolved in the coolant. Measurement of dissolved oxygen is therefor important. Oxygen concentration is minimized by introduction of hydrogen gas into the coolant. Hydrogen acts as a corrosion inhibiter by combining with the oxygen under reactor conditions to reduce the concentration of oxygen; hence the measurement of dissolved hydrogen is also important. Hydrogen concentration is also a measure of core damage and hence becomes increasingly important in the event of an accident. The measurement of the total dissolved gases is also customarily performed. Radio-active materials present in the coolant are primarily present in the form of noble gases, and activity measurement is obviously necessary from a health and safety standpoint. Boron is used in the primary coolant as a moderator to control the fission process by introduction as boric acid; hence the concentration of boron must also be determined regularly.
Except in the case of oxygen determination, which is measured by a probe in a flow cell connected in line with the primary coolant, it is necessary to draw samples of the primary coolant for analysis purposes to determine the remaining components. A shielded sampling room is provided for this purpose. The primary coolant flows through a line in the sampling room, such that samples of the pressurized coolant can be drawn for subsequent analysis outside of the containment. Typically samples on the order of 500 ml are used.
In the event of a nuclear accident continued regular analysis of the primary coolant, as well as of the containment atmosphere and of the stack vent to the atmosphere is essential, even more so than during normal operation. In the event of an accident, however, the radioactivity of the primary coolant may be increased by several orders of magnitude, for example 10,000 times. Under these conditions human access to the sample room is out of the question, and an alternate means of sampling the primary coolant must be provided.
It is thus a principal object of this invention to permit post accident withdrawal of samples of the primary coolant outside of the sampling room and to permit analysis of such samples without harmful exposure to personnel or the environment. It is also an object of this invention to provide a simple apparatus and method for determining dissolved gases in a pressurized coolant, as well as for isolating liquid and gas samples to permit subsequent analysis for hydrogen, total activity, chloride and boron under conditions minimizing exposure to personnel and the environment.
In order to carry out this invention the wall of the sampling room is modified to permit temporary diversion of a representative stream of primary coolant from the sampling room into a shielded compartment on the exterior wall of the sampling room. Doors are provided for access to the shielded compartment for the purpose of operating a diverter valve located within the sampling room temporarily to produce flow of primary coolant through piping, also located within the shielded compartment, and for the purpose of introducing a sample cask into the compartment for receiving a sample from the external piping to which the sample cask is temporarily connected. After the sample is collected and temporary flow stopped, the cask is removed and transported to the location of the test equipment.
In accordance with this invention analysis apparatus housed in a shielded case having a lead glass viewing window is utilized to withdraw the sample of coolant from the sample cask and dilute the sample with water and air thereby lowering the concentration of the activity of the sample. The apparatus contained within the case is designed to measure dissolved gases much in the manner of the conventional Shirley rig and thereafter to separate the diluted gases from water in a collection zone from which a minute, e.g. 1 .mu.l, sample can be withdrawn through a septum for analysis by gas chromotography for hydrogen and by gamma spectroscopy for noble gases.
The analysis apparatus is also arranged to deliver a sample of the diluted liquid coolant to a beaker contained within the case in which chloride is determined utilizing electrodes positioned in the beaker which are electrically connected externally of the case to make the chloride determination. Provision is also made for withdrawal of a small amount, e.g., 1 ml of the liquid from the beaker for immediate dilution on the order of one thousand fold for determination of boron by plasma emission spectroscopy. The same liquid sample with further dilution is also used for determination of liquid isotopes. The prior stripping of the dissolved gases removes a substantial portion of the activity, which is contained primarily in the noble gases. Consequently the removal of a sample as large as one milliliter of diluted coolant does not pose a serious health hazzard.
The apparatus is further provided for delivering the withdrawn and diluted sample to a shielded waste cask subsequent to analysis.
The entire operation is arranged such that collection of the sample and delivery to the analysis apparatus can take place in less than one hour and such that the total time required for analysis is also less than one hour.
The analysis apparatus contained within the shielded case is basically a modification of the conventional Shirley rig heretofore utilized in determining dissolved gases. Essentially the apparatus contains conduits and valves for connection to a sample vessel contained within the sample cask, one connection being to the lower end of the vessel in the cask and the other to the upper end. A fluid circuit is completed which includes, within the analysis apparatus itself, a reversible pump capable of operation in a forward mode, a reverse mode and a neutral mode. In the forward mode the coolant liquid in the sample is drawn through the apparatus by the pump from the upper end of the sample vessel into the apparatus cyclically to mix the sample with the water and air contained within the apparatus.
The pump is then put in the neutral mode, in which communication through the pump is open, and an expansion apparatus is connected to the fluid circuit at a low point such that it is in communication with the liquid in the circuit. The expansion apparatus has a graduate or other receiver which is open to the atmosphere at its upper end. The dissolved gases separate from the diluted coolant causing liquid to rise in the graduate or other expansion receiver thus providing a measure, by the liquid level in the receiver, of the total dissolved gases in the sample.
The connection to the expansion apparatus is then closed, and a gas collection device is switched into the fluid circuit at a level above the horizontal level of the pump. The pump is again activated in its forward mode withdrawing fluids from the top of the sample vessel and from the upper end of the gas collection device, and returning the fluids to the bottom of the sample vessel. When the added air from the gas collection device has been thoroughly mixed with the other fluids, the pump is stopped, i.e. placed in the neutral mode. The liquids then settle entraping gases within the gas collection device. The gas collection device itself is provided with a septum to permit withdrawal of small amounts of the gases which are then removed through an opening in the shielded case for the apparatus for subsequent analysis.
The connection between the pump and the gas collection device is then closed; a vent to the atmosphere is connected to the upper end of the gas collection device; and the pump is actuated in the reverse mode to draw air through the system into the upper end of the sample vessel and withdraw liquid from the lower end of the sample vessel and discharge it through a flexible tube into a beaker contained within the shielded case. The beaker is provided with suitable electrodes for determining chloride.
Subsequent to determination of chloride a sample of the contents of the beaker is withdrawn through an opening in the case for boron analysis and liquid isotope analysis. The pump is then operated in the forward mode to withdraw the contents from the beaker and discharge them to the waste cask .